Pressure-sensitive adhesive tapes such as packing tapes and surface-protective tapes and pressure-sensitive adhesive labels, seals, and sheets, etc. for industrial and office use are produced by applying a pressure-sensitive adhesive composition predominantly containing an elastomer and a tackifier resin onto a backing support such as polyethylene film, polyester cloth, or kraft paper.
In recent years, use of a hot-melt and solvent-free pressure-sensitive adhesive composition has been recommended, from the viewpoint of environmental regulations, conservation of energy and resources, and other issues. In this connection, a styrene-isoprene-styrene block copolymer has been widely employed as the elastomer used in such a pressure-sensitive adhesive composition.
Pressure-sensitive adhesive compositions are required to have excellent adhesion performance such as initial bond strength, peel strength, and holding power. In addition, demand also exists for a pressure-sensitive adhesive composition which, even at relatively low temperature (e.g., at a cold place or in a refrigerator), exhibits minimal drop in initial bond strength and peel strength.
With the aim of attaining such performance of the pressure-sensitive adhesive composition, there is disclosed a pressure-sensitive adhesive composition containing a styrene-isoprene-styrene block copolymer and a styrene-isoprene diblock copolymer (see Japanese Patent Application Laid-Open (kokai) Nos. 63-178187 and 63-178188 and Japanese kohyo Patent Publication No. 2001-504519). In addition, a pressure-sensitive adhesive composition containing a styrene-isoprene-styrene block copolymer and a styrene-butadiene block copolymer has also been proposed (see U.S. Pat. No. 5,290,842).
However, the aforementioned pressure-sensitive adhesive compositions have drawbacks that excellent peel strength at ambient temperature drastically drops at low temperature and that holding power is poor.